Generally, a railroad includes at least one pair of elongated, substantially parallel rails coupled to a plurality of laterally extending ties and which are disposed on a ballast bed. The rails are coupled to the ties by metal tie plates and/or spring clips. The ballast is a hard particulate material such as, but not limited to, gravel. Ties may be made from either concrete or wood. The ballast filled space between ties is called a crib. Concrete ties are typically spaced about twenty-four inches apart, whereas wood ties are spaced about nineteen and a half inches apart.
During installation and maintenance various operations must be performed at each tie location. For example, ballast must be “tamped,” or compressed, to ensure that the ties, and therefore the rails, do not shift. A tamping device, not surprisingly called a “tamper,” typically consists of at least two pairs of work heads mounted on a motorized vehicle structured to travel on the rails. A work head includes a pair of elongated, vertically extending tools structured to move together in a pincer-like motion as well as being structured to move vertically. The tools, preferably, have two prongs spaced so that each prong may be disposed on opposite lateral sides of a rail. The work head further includes a vibration device structured to rapidly vibrate the tools. In this configuration, a work head may be disposed above a tie with one tool on either side of the tie. Further, the prongs of each tool are disposed on either sides of the rail. Thus, a tool prong is disposed above, and just outside, of each corner of the rail/tie interface. At least two work heads are used so that one work head may be placed over each rail.
Initially, the tools are generally vertical and parallel to each other. When actuated, the tool head moves vertically downward so that the tips of the tools, that is the tips of the prongs, are inserted into the ballast to a predetermined depth that is, preferably, below the bottom of the tie. The tools are then brought together in a pincer-like motion thereby compressing the ballast under the tie. Actuation of the vibration assembly further compresses the ballast under the tie. Once the vibration operation is complete, the tools are returned to a substantially vertical orientation and lifted out of the ballast. The tamper then advances to the next tie and the operation is repeated. Typically, a tamping operation lasts about three seconds.
The act of advancing the tamper to the next work location may be called “indexing.” Indexing may be performed one tie at a time, or multiple ties at a time. For example, some tamping machines include a set of tamping tools at the front end of the rail vehicle and another set of tamping tools at the back end of the vehicle. After identifying a tie at the work site as the first tie, the front set of tamping tools may work upon the “odd” ties and the back set of tamping tools may work upon the “even” ties. In this situation, the tamper vehicle would index, i.e. move forward, two ties at a time. The tamper vehicle, as well as other rail installation and maintenance vehicles, typically locates the tie/rail interface by locating the tie plate that connects the rail to the tie, e.g. by utilizing a metal detector that travels beside the rail.
On conventional indexing machinery, such as, but not limited to tampers, the equipment starts and stops at different intervals as required by the work that has to be performed. In most railroad applications, the indexing motion of different machines is dictated by the tie spacing. Most of the work required on the track is usually performed at each tie location, i.e., tamping of the ballast supporting the ties, lifting and lining of the track panel, spiking of the tie plates for fastening the ties to the rail, anchor removal and/or application, plugging of spike holes, clip application and removal, etc.
Conventional equipment performing track maintenance consists mostly of machines carrying one or two operators. These machines accelerate (under their own power), to the ties requiring work. As they approach the tie, they rapidly slow down to a stop, perform the required work and index to the next tie to repeat the cycle. This work is performed sometimes at a cycle rate of less than three seconds. During this acceleration and deceleration, the operator is being pushed backward and forward by the dynamics of the machine he is riding. The operator is working in a very uncomfortable environment, subject to fatigue, stress and difficulty to perform the required duties of his work.
One existing machine designed to alleviate the problem on the operator, consists of splitting the machine in two segments: one half of the machine does the indexing and a first work function while the other half moves at a constant speed while sometimes performing a different work function. The operator sits on the continuous moving portion of the machines. This system is normally employed on large machines and works in a satisfactory manner, however, the system is very expensive and cumbersome. For example, two different machines and two drives are required, the system is not practical for smaller and lighter machines due to the additional weight required to achieve an effective tractive effort, and the system requires sophisticated electronics required to control the motion of the two segments relative to each other. That is, without sophisticated electronics controlling the motion of the two segments, the two segments may collide and damage each other and/or injure an operator.